The present invention relates to a method for coating of a sheet-like cellulose material, such as paper or cotton fabric, by applying a composition comprising at least one glucan having a β(beta)-1,3-glycosidically linked main chain and at least one side group having a β(beta)-1,6-glycosidic bond to the main chain. One preferred glucan is Schizophyllan. The composition often comprises at least one solvent and can be applied onto the surface of the cellulosic material. The invention is further directed to a coated sheet-like cellulosic material.
Furthermore, the present invention is directed to a composition comprising at least one glucan, particularly Schizophyllan, and at least one ionic liquid.
Paper and paper products (e.g. board) are known for their hydrophilic properties which can be regarded as a disadvantage in many application areas. Often the paper surface is treated by coating or sizing in order to improve the hydrophobic properties and quality of the paper (e.g. printability, dimensional stability). The so called “sizing” renders the paper surface more hydrophobic and prevents or delays the penetration of water and ensures dimensional stability. This is important for all types of printing paper but also for packing paper and board. Commonly used “sizing agents” are for example rosin size, alkyl ketendimer (AKD) and alkenyl succinic anhydrid (ASA).
For ecological and economic reasons, there is a strong interest in bio-based coatings for paper in order to enhance the barrier properties against water and oil and thereby to broaden the application areas of paper and paper products in which hydrophobic or even highly hydrophobic surfaces are needed.
It is commonly known in the state of art that several glucan compounds, such as starch, can be used in coating and sizing of paper. The document U.S. Pat. No. 7,348,065 describes a coated paper with improved slipping properties, wherein the coating comprises a olefin-carboxylic acid copolymer and a second polymer selected from starch, cellulose, polyvinyl alcohol, polyacrylamide or sodium alginate.
U.S. Pat. No. 5,348,065 discloses a process for the treatment of paper using a degradation product which is a mixture of oligomers of a polysaccharide derivative, such as carboxymethyl cellulose or carboxymethyl starch, wherein the treatment can for example encompass impregnating of pulp or coating of a paper product.
Generally, polysaccharides consisting of many glucose units (D-glucose) are referred to as glucans. Common glucans are e. g. cellulose and starch. Cellulose essentially consists of glucose units, which are linked β(beta)-1,4-glycosidically. Starch essentially consists of glucose units, which are linked α(alpha)-1,4-glycosidically and optionally have α(alpha)-1,6-glycosidic linked side chains.
Glucans which have a β(beta)-1,3-glycosidically linked main chain and side groups, having a β(beta)-1,6-glycosidic bond to the main chain are secreted by various fungal strains. For example, the so called “Schizophyllan” is produced by the fungus Schizophyllum commune, a basidiomycete, which exhibits filamentous growth and secretes during growth inter alia said glucan product. Aqueous solutions of such polysaccharides exhibit advantageous physiochemical properties (e.g. high viscosity, stability to high shear rates, stability to high temperatures and to high salt concentrations).
In addition to Schizophyllan, the organism Schizophyllum commune secretes other major biopolymers into a liquid growth media, namely the peptide hydrophobin (24 kDa) and a further protein (17 kDa), which is also found in the fungal cell wall.
Commonly, Schizophyllan can be described as a polysaccharide with repeating units consisting of three β(beta)-1,3-linked D-glucose units as a backbone, one of which is linked to single D-glucose molecule through β(beta)-1,6-linkage.
The structure of the repeating unit of Schizophyllan can be described by the following formula:

The typically molecular weight Mw of Schizophyllan is in the range of about 5·106 to about 25·106 g/mol.
The preparation of said glucans by fermentation with the fungus Schizophyllum commune is for example described in EP-A 271 907, EP-A 504 673 and DE-A 40 12 238.
Another example for glucans which have a β(beta)-1,3-glycosidically linked main chain and side groups having a β(beta)-1,6-glycosidic bond, are the so called homo-polysaccaride “Sceleroglucan”, which is e.g. secreted by the fungus Sclerotium rolfsii. 
Many fungal stains secreting said glucans are known to the skilled person. Examples comprise Schizophyllum commune, Sclerotium rolfsii, Sclerotium glucanicum, Monilinia fructigena, Lentinula edodes or Botrytis cinera. Glucan producing fungal strains are further described in EP-A 271 907 and EP-A 504 673.
Schizophyllan generally has a network structure and high molecular weight and hence can for example be used in applications in which high viscosities and/or increased binding is needed. Schizophyllan has been extensively studied as a viscosity-control agent (Fang et al., Biomacromolecules, 2005, 6, 3202; Kony et al., Biophys. J., 2007, 93,442).
The publication G. Martin et al., Biopolymers, 1999, 49, 621 describes that the fungal protein hydrophobin and also the fungal culture supernatant of Schizophyllum commune comprising hydrophobin and Schizophyllan can form a stable coating on both hydrophobic and hydrophilic surfaces.
U.S. Pat. No. 5,215,681 describes concentrated liquid solutions of polysaccharides prepared by ultra-filtration of a dilute solution of polymer to which a surface-active agent has been added. The polysaccharide can for example be Sceleroglucan or Schizophyllan. These solutions can be used as thickening agent, e.g. in the recovery of hydrocarbons.
Other applications include carriers for metals and pollutants in natural water and the stimulation of the human immune system. Schizophyllan is normally reported to have a high stability (up to 120° C. in aqueous solution), high water solubility and poor gelling ability. It is also known for its non-toxic and biocompatible nature. In addition, Schizophyllan has been reported to form brittle and weak gels and to be used in fabrication of nano-fibre structures.